WG1 – WG2

1. Future Circular Collider Study Kickoff Meeting Geneva, 14th February WG1 – WG2 Launching the main activities Roberto Tenchini

2. WG1 – main physics objectives • Understand the experimental precision with which TLEP could measure all electroweak observables by accumulating 1012 Z bosons without longitudinal beam polarization. • Set constraints on the size of the sample needed with longitudinal beam polarization, as a function of the polarization level, to make it relevant in the physics programme of TLEP. • (A priori the observables are not limited to the ones of LEP, SLC)

3. WG2 – main physics objectives • Understand TLEP potential to measure all observables related to multi-gauge-boson production (di-boson WW, ZZ, Zg or gg production, but also tri-boson production like WWg, WWZ, ggg, WWH, etc.) above the Z pole. • Define a strategy for optimal W mass measurement (scan of the WW threshold, direct measurement), and for other W properties, such as width and branching fractions. • Investigate the use of Z radiative returns for the measurement of the Z invisible width and the beam energy

4. The starting point: our legacy • Data collected by LEP, per experiment: • about 150 pb-1, (4·106 hadronic Z)at the Z peak • about 700 pb-1 above the WW threshold (104 WW pairs) • Data collected by SLC: • About 150000 Z at 77% polarization qq() 100 pb WW 17 pb 1 pb ZZ

5. WG1: a subgroup on lineshape • Understand the precision on centre-of-mass energy for the mass (LEP ~2·10-5) and the energy spread for the width • Understand precision on luminosity determination (LEP ~ 610-4) • Check other aspects, e.g. is the theoretical description of the lineshape still adequate ?

6. WG1: a subgroup on Asymmetries • Long standing difference between Alr and AFB(b), it must be sorted out • Understand the potential for a measurement of Alr with polarized beams • Understand the potential for a direct measurement of the b couplings (again need polarization) (include Rb here)

7. WG2: subgroup on precision measurement of the W mass • Understand how to perform a precise measurement from the WW threshold scan • Revisit the LEP2 method of direct reconstruction (there is room for improvement, e.g. beam energy, large statistics on semileptonic events, etc. )

8. WG2: subgroup on triple and quartic boson couplings • Understand TLEP potential, taking into account that LHC has already reached LEP precision for the charged triple gauge couplings (neutral and quartic couplings are even better).

9. Radiative return WG2: subgroup on Z radiative returns • Study the use of radiative returns for the determination of the beam energy (extend the study to other dibosons) • Understand the precision which can be reached for the Z invisible width

10. Proposal for initial subgroups(can split them in the future) • WG1 (a) : Z lineshape • WG1 (b) : asymmetries at the Z • WG2 (a) : W mass and W properties • WG2 (b) : Triple and quartic couplings • WG2 ( c): Z radiative returns

11. Some objectives of subgroup work • Understand achievable precisions and limitations (e.g. measurement of non- electroweak observables, measurement of the beam energy, measurement of the longitudinal polarization, theoretical uncertainties, etc.), and contribute to proposing ways to alleviate them. • Set constraints on the performance and the relevance of the various sub-detectors, as well as on the experimental environment, to make the experimental precision match or approach the expected statistical accuracy. • Define the software needs to make possible these measurements and their interpretation with the required precision (online, generator, simulation, reconstruction, analysis, global fits, ...).